Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$17.38	8.459%	$18.8502	$18.85	$18.85	$18.90
Purchase #2	$175.39	4.661%	$183.5649	$183.56	$183.55	$183.60
Purchase #3	$110.25	7.781%	$118.8286	$118.83	$118.85	$118.80
Purchase #4	$100.61	8.740%	$109.4033	$109.40	$109.40	$109.40
Purchase #5	$16.32	12.707%	$18.3938	$18.39	$18.40	$18.40
Purchase #6	$41.90	5.732%	$44.3017	$44.30	$44.30	$44.30
Purchase #7	$206.68	5.248%	$217.5266	$217.53	$217.55	$217.50
7 purchase totals =	$668.53		$710.8691	$710.86	$710.90	$710.90